Emulsions are ubiquitous in daily life; many food products such as milk, mayonnaise or salad dressing and certain types of paints are emulsions. Droplets of single emulsions can also serve as templates to fabricate microparticles that serve as carriers for delivery purposes or building blocks of hierarchical 2D and 3D materials. Especially if used as templates to fabricate microparticles or capsules, it is important to closely control the size and composition of droplets. The extent to which these parameters can be controlled is determined by the assembly route; the most widely used techniques include bulk emulsification, membrane filtration and microfluidic assembly. Bulk emulsification techniques allow for the production of emulsion at a high throughput rendering them attractive for industrial applications. However, the control over the size of the resulting droplets is poor resulting in a broad size distribution. By contrast, microfluidic techniques enable the assembly of monodisperse droplets with a good control over their size; this is achieved through the controlled formation of a single droplet per time and droplet maker. However, this comes at the expense of relatively low throughput.
The low throughput limits the applicability of microfluidic technologies in industry and to produce microparticle building blocks for the assembly of new types of hierarchical 2D and 3D material despite that they offer superior control over the size and composition of droplets. For many applications, membrane emulsification techniques present an attractive compromise; their throughput is considerably higher than that achieved with microfluidic techniques while the size distribution of droplets is significantly lower than that of droplets produced through bulk emulsification routes. However, the polydispersity of droplets produced through membrane emulsification techniques increases with increasing average size of the droplets. Thus, the production of monodisperse droplets at a high throughput is still a major challenge.